Isomerization process



June 17, 1947. G. L. FARRAR ISOMERIZATION PROCESS sslneets-sheet 1 Filed001:. 23, 1944 5 1m 4 XML WW5. a m MA w w lwm J 2 0 0 Im 1 1 0 0 0. w 00 0 0 H. w a. w 2 w 0 0 o 0 0 0. 0 0

ALUIJlNU/V BRO/HIDE CONCENYRITIOM MOL FIG. 1

Gerald L.- Farrar June 17, 1947. e. L. FARRAR ISOMERIZATION PROCESSFiled Oct. 25, 1944 3 Sheets-Sheet ,2

ONCE-THROUGH G4T4LYS'T LIFE BBLS. iC PRODUCED /100 LBJ. A1813. CONSUMEDa o w 000 o 0 o o a o 00 0 mm M wmwww w 2 m 5 5% 64mm Rein QSE QZVRRSQFIG. 2

Gerald L IZ'zrrar INVENTOB ATTO June 17, 1947. G. FARRAR I 2,422,346

ISOMERIZATION PROCESS Filed Oct. 23,. 1944 5 Shee'ts-Sheet 3 Gerald L.Fa rrar MA/T012 ATTOR hatentecl June 1 7, 1947 assignments, toSmelly-Vacuum Oil Company; Incorporated, New York, N; Y. a corporationof New York Application October 23, 1944, Serial 559,921

9 Claims. 1

This invention relates to the isomerization of normal butane toisobutane. Specifically this in vention is concerned with a process forconverting normal butane toisobutane involving the use of aluminumbromide promoted by oxygen as catalyst fo the conversion. Moreparticularly the invention concerns the use of optimum concentrations ofthe aluminum bromide catalyst when operating the isomeriZation processwithin a preferred range of conditions with respect to temperature andconcentration of oxygen pro moter.

It is known to isomerize normal butane to isobutane in the presence ofaluminum halides such as aluminum chloride and aluminum bromide. It isalso known that these catalysts require promoters such as hydrogenhalides, alkyl halides and free halogens in order to accelerate thereaction to rate levels which are consistent with economic commercialoperation. The use of oxygen as a promoter for activating aluminumbromide catalyst for the isomerization of normal butane to isobutane istaught and claimed in the copending application of Alex Gr. Oblad,Ed'W-in M. Irish and Manuel H. Gorin, entitled Hydrocarbon conversion process,Serial 513,180, filed December .6, 1943.

The object of the present invention is to provide an improved processfor aluminiun bromide isomerization of normal butane by accelerating thereaction rate. Another object is to accelerate the reaction rate bymeansof oxygen promoter for the aluminum bromide catalyst. A morespecific object of the invention is to correlate the amount of aluminumbromide catalyst added to a continuous oxygen promoted aluminum bromidebutane isomerization process with the temperature employed in suchprocess and with the amount of oxygen added to such process therebyobtaining the optimum conversion per passwith a minimum consumption ofcatalyst and minimum production of butane decomposition products. Stillanother object of the invention is to obtain a maximum increase of thereaction rate in normal butane isomerization without resorting toexcessive temperature and excessive use of catalyst promoter. These andother objects will become apparent from the description of theinvention'whic'h fol lows.

Butane ,isomerization using oxygen promoted aluminum bromide catalyst isa unimolecular first order reaction. Thus the isobutane concentration inthe feed and residence time in the reactor have no effect on thereaction rate and the reaction rate for the continuous process maybecalculated from the equation eao where 2 KiFirst orde react on rate' nsa t p es d in u i s per 110.111, f ctor feed d ivin for 1- e. i rium pere t iso C1 minus r S 4 n t V .r'eaGtOr feed, Fe=Reactor driving force,that is, equilibrium percent iso C4 minus percent iso C4 in the react r.an :E'esijdenc e time or time of hydrocarbon contact in the reactorexpressed in hours.

Opera n vari es inmy on n proc s which efiect the value of K in theabove equation are temperature, concentration of the alumi um om decatal st. m un of o y en e to activate the catalyst and intimacy ofcontact of the oxygen'with the hydrocarbon solution of the promotedaluminum bromide catalyst. Generally speaking the higherthe operatingvalue of K the more e fiicient will be the process particularly withrespect to capacityof a given unit. However, other {actors such ascatalyst consumption and availability of facilities for recovering thecatalyst, the requirement for relatively high pres,- sure equipment whenoperating in the higher temperature ranges and other operating costsshould be considered in determining the rate constant for most efficientoperation of a continuous process using oxygen activated aluminumbromide catalyst.

The efiect of increasing the temperature on the reaction rate wheniilierating in the presence ofoxy'g'en activatorjfo'rtheicatmyst is mostmarked in the 'if'an'g'e of norm about F. to aboutZOO" F.1'ahd1bf .omslsis'a hi her tem eratur s with best fsillts obtained at BJbDU-t 225 F.While g e t mperature ip 17116 r t ca t mpt atures'of the reactants, i.e., about 300 F. may

be used, I'prereritdoper e'attemperatures within the range of from about210 F. to'about 240" F. and thereby avoid the use ,of the hi herpressure ieTqU'ipment, Operation at temperatures ov about 250 F. tend tomot rackin and the production o an increased a oun o ydroca ons boil nabove m e ow heboilnt ran e/of the-butan ifrac n- This i u desirable'where [the process is primarily concerned with the man c ure of .iscutane from norma butan by the u i i 'at c or a o ub e catalyfi The amounof ox en r qui ed to om t aluminu b m de ly 't io 'ihutan ii m at n isrela ively smal If oxy en i d d in ap r ciah cg r fi y. r at velv'la eamou t luminum b omi e c t ly t are con umed and hence all ex ss' b ethe abso ute re ui emen is t e av ide I bareiound tha th amo nt of xy enreq red i clo l el ted to'th riee react on space. that is. th 'v urne' ohe eac o e iup by t e rea tin liqu dibutan or other words theltotal' vme DI he ea to t e yolumeoc'cun ed "by iheipackinsimaterialr Whening-s46 operating my process under conditions Where catalyst recoveryfacilities are not sufficient to recover consumed catalyst efficiently,the amount of oxygen addition will lie within the range of from about0.005 to about 0.2 pound mols of oxygen per hour per thousand barrels offree reactor space. Larger amounts of oxygen up to 2.0 pound mols perhour per thousand barrels of free reactor space may be used where theeconomics of catalyst recovery are suificiently favorable to justify theincreased catalyst consumption resulting from greater use of oxygen inorder to obtain a high reaction rate.

A third factor influencing the value of the reaction rate constant K inthe above relationship is that of aluminum bromide concentration in thereactor. I have found that there is an optimum range of catalystconcentrationin the normal butane reactant to obtain maximum reactionrate which optimum is independent of the amount of oxygen promoter usedand also independent of the temperature of operation over the operatingrange contemplated by my process. In Figure 1 plots of reaction rate Kvalues versu mol percent concentration of aluminum bromide catalyst areshown for Oxygen addition values within the above specified ranges. Thetemperature of operation used in obtaining data from which Figure 1 isplotted was 225 F. Data obtained at other temperatures within the abovebroad range of 170 to 300 F. indicate that the optimum is approximatelythe same for the entire temperature range of operation, particularly thepreferred temperature range of 210 F. to 240 F. The optimum catalystconcentration is from about 2.1 mol percent to about 2.85 mol percent ofaluminum bromide in the reactants and I prefer to operate my process tomaintain this concentration of aluminum bromide catalyst in thereactants in the reaction zone.

In Figure 2 is shown the effect of oxygenaddition at various levels ofonce through conversion on isobutane production and catalyst life whenoperating a reactor packed with Raschig rings for a reactor having afree volume of 1000 barrels, and at a temperature of operation of 225F., that is, within the preferred operating range. The concentration ofisobutane in the reactor feed is assumed to be five mol percent and theconcentration of aluminum bromide in the reaction space is within theoptimum range, i. e., 2.5 mol percent. With these factorsafiectingconversion held constant, the isobutane production in barrelsper day is plotted against once-through catalyst life expressed asbarrels of isobutane produced per 100 pounds of aluminum bromideconsumed, for various parameters of oxygen feed in pound mols per hourand parameters of reactor once-through conversion expressed as molpercent of isobutane produced. Thus, for example, if it is desired toproduce 1000 barrels of isobutane per day by operating the above reactorunder the specified conditions relative to temperature, catalystconcentration and feed composition, a once-through conversion ofapproximately 18 mol percent of total reactor feed to isobutane willresult in the production of 100 barrels of isobutane per 100 pounds ofaluminum bromide catalyst consumed. The oxygen added to maintain therequired reaction rate will approximate 0.12 pound mols per hour. On theother hand, if facilities for recovering the consumed catalyst areavailable, I may. operate the above reactor at, for examp1e,approximately 37 mol percent conversion per pass by the addition 4 ofabout.0.30 pound mols of oxygen per hour with a catalyst life of 45barrels of isobutane per 100 pounds of aluminum bromide consumed. Higherconversion per pass results in an obvious economy in fractionation coststo recover the product isobutane, and the choice of rate of oxygenaddition and throughput must be balanced against fractionation costs andcatalyst recovery costs in the selection of the operating conditionsactually chosen within theranges proposed. In general the operatingconditions should be selected to give a 5 to 40 mol percent, preferablya 15 to 30 mol percent, production of isobutane per pass through thereactor. Residence time will usually fall within the range of /2 to 12hours the preferred range being 2 to 8 hours to obtain conversionswithin the above range. 7

Referring now to Figure 3, wherein is shown a diagrammatic embodimentofmy process, liquid normal butane or a liquid C4 paraflinic hydrocarbonstream containing 70 to 100 mol percent but preferably at least molpercent of normal butane is passed by means of pump l0 through line H tocatalyst mixer l2 whereinraluminum bromide catalyst, introduced to thebutane stream through valve l3 in line I4, is thoroughly mixed by meansof mechanical stirrer I5 with the hydrocarbon stream to-produce completesolution of the catalyst. If desired, fresh make up aluminum bromidecatalyst may be introduced to the system through valved line l6 whichleads from line H to recycle line H. The aluminum bromide may beintroduced to the system through line M as a hot concentrated solutionin normal butane and the concentrated solution may then be diluted tothe desired range of from about 2.1 mol percent to about 2.85 molpercent by the main normal butane feed stream in line The normal butanestream containing an amount of aluminum bromide within this range ispassed through line l8 at a pressure of from about275 pounds to 325pounds per square inch to heater I9 where it is raised in temperature tothe range of from about 210 F. to about 240 F. whence it passes via line20 to be introduced to reactor 2| at a point near or at the top of thetower.

Tower 2| which preferably represents a bank of multiple reactors mayconsist of unpacked towers provided with suitable mixing means forcontacting the normal butane solutionrof aluminum bromide with freeoxygen. Preferably the reactor system is packed with ceramic typepacking such as unglazed porcelain or other inert packing material toobtain a large surface to volume ratio. As indicated hereinabove theamount of oxygen promoter required is relatively. small. Assuming thefree reaction space in reactor2| to be one thousand barrels with a ratedcapacity of 1000 barrels production of isobutane per day at twentypercent conversion per pass, only 0.127 pound mols, i. e., approximately4 pounds, per hour of oxygen are required to activate thedissolved'aluminum bromide catalyst. Oxygen may be admitted to thereaction chamber 2| by injection to feed line 20 either continuously orintermittently from line 22 or, if desired, itfmay be injected directly,to reactor 2| or to circulation line 23 from line 24 which joins line22. Contact of theoxygen with liquid butane containing dis solvedaluminum bromide in tower 2| is made possible by continuouslywithdrawing a stream of the reacting liquid mass from tower 2| throughline 23 and circulating it to the top of the tower by means of pump 25.The rate of circulation for most satisfactory results may be expressedin Reynolds numbers determined on g a hydraulic radius ibasis. Reynoldsnumbers of from about 500to about 5,000 givte satisfactory contact whenthe tower. is packedwith unglazedceramic ware ofihigh surfaceto volume.ratio. The concentration. of aluminum. bromide in tower 2 I. ismaintained at about 2.5 mol percent and with conversionat :20.percenttheresidence time in tower 2! will be approximately 4.8 hours.

.The mixture of'normal butane and isobutane is withdrawn. from .thereaction cycle. through line by operation of pressure release valve3l..and iscooled incooler 32 toa temperaturewithin the rangetof from.about 145 to about.175 F. The product. is then. passed by valve line 33to flash tower catalyst concentraton34-whereinapproximately-75'percentof the liquid is flashed leaving 25 percent forrecycle with dissolved catalyst directly to reactor 2i through line 35and recycle line H. I

When operating my process at relatively low conversion perpass there isvery little of C5 and and higher hydrocarbons formed. However, even asmall; conversion to these higher molecular.

Wei ht hydr carbo s e s t cause their cu lation in a systen' whereincatalyst and unconverted normal butane are recycled to the reactor. Thegreater part of the small amount of C and higher hydrocarbons flashesoff with the butanes r m fl h-tap r. 3 the. m x vapors p si Z F EQUEh-UQ3Q ZQ c n e er 31 whence ndensate is picked upby pump38 in line 39 fortransfer to storage or preferably to fractionator 40 by' lines 4| and43. Ingfractionator lilisobutane produonwhioh is taken overheadv throughline 44, is separated, from normal butane and any higher boilinghydrocarbons. Normal butane .is.withdrawn for recycle to tower 2| as asidestream through line which. connects with recycle line I! and thehigher boiling hydrocarbons, if any, are withdrawnlthrough line 46. .Ifno hydrocarbons boiling higher than the butanes are formed, normalbutane may be withdrawn as the bottom product for recycle through line46 which also connects with recycle line [1. When operating in thismanner, flash tower concentrator 34 may be by-passed by closing thevalve in line 33 and opening valve 42 in line 43. Thus, assuming noproduction of C5 and higher hydrocarbons, and the capacity of thehereinabove described unit to be 1000 barrels per day of 100 percentisobutane from 1000 barrels per day of 100 percent normal butane feed,and a reactor system 2| containing 1000 barrels of free reaction space,the following quantities of butanes per hour will be handled inoperating with valve 42 open and the concentrator by-passed. Throughfeed pump I0 will flow 41 barrels of fresh normal butane and 166 barrelsof recycle normal butane, the total of 208 barrels being subjected to aresidence time of 4.8 hours in reactor 2|. 166% barrels per hour ofnormal butane recycle with dissolved aluminum bromide catalyst will behandled as the bottom draWoiT from fractionator 40 through line 46, and41%, barrels of isobutane per hour will be recovered as overhead productthrough line 44, from the 208%; barrels of product per hour being sentto fractionator 40. If, on the other hand, C5 and higher hydrocarbonsare produced, accumulation of these products may be substantiallyprevented by flashing the product in catalyst concentrator 34 in whichcase as a result of the partial recycle of isobutane product, the loadon pump I 0 will be increased from 208 barrels per hour to approximately222 barrels per hour assuming. afiash separation inconcentrator' 34 ofseventy-five. percent or the liquid product as overhead. 4 Ifconcentrator is, eliminatedem tirely, normal butane recycle may bewithdrawn from tower .40..through line 45 and. the bottom fraction fromtower .40 comprising C51 andhigher hydrocarbons may:be.-subjected: tofractionation in a separate towerfor separation =o-f1'the aluminumbromide catalyst fo'rthese higher boiling hydrocarbons, aluminum bromidebeing recycled independent of the normal-butane recycle stream.

H AlthoughI havedescribedmyinvention as ap. plicableto a continuousprocesswherein. the isomerization 1 is carried out in a. packed tower, Ido not wish to be limited to this type of reactor orto continuousoperation. Reactors containing no packing may be used ifmeansforsproducing intimate contact ofthe normal butane solution ofaluminumbromide catalyst with the oxygen activator is provided. Optimumcatalystconcentration is applicable to non-packed reactor continuousoperation as'wellas to batch typeoperation.

1. Inaprocessfor'the conversion of'liqui'd-nor mal butane to isobutanein a raction zon'e whereinsaid normal' butane ismaintained' in intimatecontact with an aluminum bromide catalyst promoted by free oxygentheimprovement which comprises maintaining in solution in said butane andisobutane a concentration of aluminum bromide greater than 2.1molpercentandnotgreater than I 2.85 mol percent of saidsolution andmaintaining said solution at a temperature' within the range of iromabout210 F. to about'240fF;

2. a continuouszprocessfor increasing the isobutane content of a liquidpredominantly/ normal butane stream wherein aluminum: bromide catalystis added to said liquid stream and where in said aluminumbromide-containing stream is maintained in intimate contact with freeoxygen in a pocked tower reactor whereby said aluminum bromide isactivated while in contact with said liquid stream the improvement whichcomprises dissolving said aluminum bromide in said predominantly normalbutane stream in amounts such that the aluminum bromide in solution insaid butanes in said packed tower reactor is maintained at aconcentration greater than 2.1 mol percent and not greater than 2.85 molpercent of said solution and maintaining said solution at a temperaturewithin the range of from about 210 F. to about 240 F.

3. The process of converting normal butane to isobutane comprising thesteps of 1) dissolving aluminum bromide in a liquid normal butanestream, (2) passing said liquid normal butane through a packed reactorwherein the temperature is maintained within the range of from about 210F. to about 240 F. and maintaining the pressure in said packed reactorsufiiciently high to maintain the normal butane in the liquid phase, (3)continuously passing an oxygen containing gas in intimate contact withsaid normal butane and said aluminum bromide in said packed reactor, and(4) regulating the amount of aluminum bromide dissolved in step 1 tomaintain aluminum bromide in the solution in said packed reactor at aconcentration greater than 2.1 mol percent and not greater than 2.85 molpercent of said solution.

4. The process of claim 3 wherein the amount of oxygen added to thereactor is within the range of from about 0.005 to 0.20 pound mols perhour per thousand barrels of free reaction space.

The process of claim 3'wherein the oxygen containing gas of step .4 isselected from the class consisting of air and commercial oxygen gas.

6. The process of claim 3 wherein the packed reactor is substantiallycompletely filled with an inert ceramic packing material.

7. The process for the isomerization of normal butane to isobutane whichcomprises introducing normal butane into a reaction zone containing asolution of aluminum bromide in an essentially four carbon atomparafiinic hydrocarbon solvent, maintaining a temperature of between210.F. and about 240 F. and a pressure at least sufiicient to maintainthe normal butane in the liquid phase at the reaction temperature insaid reaction Zone, introducing free oxygen into said reaction zone topromote the isomerization reaction, withdrawing four carbon atomparaifin hydrocarbons including isobutane product from said reactionzone, and introducing aluminum bromide to said reaction zone at a rateso as to maintain aluminum bromide dissolved in the paraflinhydrocarbons at a concentration greater than 2.1 mol percent and notgreater than 2.85 mol percent of said solution.

8. The process of claim 7 wherein the amount of oxygen introduced to thereaction zone is within the range of from about 0.005 to 0.20 pound molsper hour per housand barrels of free reaction space.

9. A continuous process for the isomerization of normal butane toisobutane which comprises introducing a normal butane containinghydrocarbon stream into a reaction zone containing a solution ofaluminum bromide in an essentially four carbon atom parafiinichydrocarbon solvent, maintaining in said reaction zone a temperaturewithin the range of from about 210 F. to about 240 F. and a pressure atleast sufiicient to maintain the normal butane in liquid phase at the 8reaction temperature in said reaction zone, intro ducing free oxygeninto said reaction zone in an amount within the range of from about0.005 to. about 0.2 pound mols per hour per 1000 barrels of freereaction space in said reactor to promote the isomerization reaction,withdrawing four carbon atom paraiiin hydrocarbons including isobutanefrom said reactionzone, introducing aluminum bromide to said reactionzone at a rate so as to maintain a concentration of aluminum bromide insolution in the paraffinic hydrocarbon solvent equivalent to about 2.5mol percent of the aluminumbromide solution in said reaction zone andrecovering isobutane from. said four carbon atom paraffin hydrocarbonswithdrawn from said reaction zone.

GERALD L. FARRAR.

REFERENCES CITED UNITED STATES-PATENTS" Number Name Date 2,271,860Goldsby Feb. 3, 1942 2,341,286 Pines et a1 Feb. 8, 1944 2,342,124Daniorth Feb. 22, 1944 2,343,406 Dryer Mar. 7, 1944 2,346,768 Laughlin lApr. 18, 1944 2,278,934 Lee Apr. 7, 1942 2,288,477 Montgomery June30,1942

' FOREIGN PATENTS Number Country Date 512,408 Great Britain Sept. 1,1939 OTHER REFERENCES

